Merge branch 'master' into urcu/ht-shrink
[urcu.git] / rculfhash.c
index d89c0cb6635ead96de12a9bdbb82d7c2b8e0a0b2..600feecfa8f4f8230eede1683cf79cff14a0333f 100644 (file)
@@ -1796,13 +1796,9 @@ void do_resize_cb(struct rcu_head *head)
 }
 
 static
-void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int growth)
+void __cds_lfht_resize_lazy_launch(struct cds_lfht *ht)
 {
        struct rcu_resize_work *work;
-       unsigned long target_size = size << growth;
-
-       if (resize_target_grow(ht, target_size) >= target_size)
-               return;
 
        /* Store resize_target before read resize_initiated */
        cmm_smp_mb();
@@ -1820,27 +1816,47 @@ void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int grow
        }
 }
 
+static
+void cds_lfht_resize_lazy_grow(struct cds_lfht *ht, unsigned long size, int growth)
+{
+       unsigned long target_size = size << growth;
+
+       if (resize_target_grow(ht, target_size) >= target_size)
+               return;
+
+       __cds_lfht_resize_lazy_launch(ht);
+}
+
+/*
+ * We favor grow operations over shrink. A shrink operation never occurs
+ * if a grow operation is queued for lazy execution. A grow operation
+ * cancels any pending shrink lazy execution.
+ */
 static
 void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
                                unsigned long count)
 {
-       struct rcu_resize_work *work;
-
        if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
                return;
-       resize_target_update_count(ht, count);
-       /* Store resize_target before read resize_initiated */
-       cmm_smp_mb();
-       if (!CMM_LOAD_SHARED(ht->t.resize_initiated)) {
-               uatomic_inc(&ht->in_progress_resize);
-               cmm_smp_mb();   /* increment resize count before load destroy */
-               if (CMM_LOAD_SHARED(ht->in_progress_destroy)) {
-                       uatomic_dec(&ht->in_progress_resize);
+       count = max(count, ht->min_alloc_size);
+       if (count == size)
+               return;         /* Already the right size, no resize needed */
+       if (count > size) {     /* lazy grow */
+               if (resize_target_grow(ht, count) >= count)
                        return;
+       } else {                /* lazy shrink */
+               for (;;) {
+                       unsigned long s;
+
+                       s = uatomic_cmpxchg(&ht->t.resize_target, size, count);
+                       if (s == size)
+                               break;  /* no resize needed */
+                       if (s > size)
+                               return; /* growing is/(was just) in progress */
+                       if (s <= count)
+                               return; /* some other thread do shrink */
+                       size = s;
                }
-               work = malloc(sizeof(*work));
-               work->ht = ht;
-               ht->cds_lfht_call_rcu(&work->head, do_resize_cb);
-               CMM_STORE_SHARED(ht->t.resize_initiated, 1);
        }
+       __cds_lfht_resize_lazy_launch(ht);
 }
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